ΟΣΤΕΟΠΕΝΙΑ ΕΞ ΑΧΡΗΣΙΑΣ

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2 Disuse osteopenia has been shown to be a regional phenomenon Disuse is one of the many reasons inducing bone loss and resulting in secondary osteopenia or osteoporosis.Disuse osteopenia has been shown to be a regional phenomenonin the areas with tremendous decrease in weight bearing like lower limbs.A. Howard, “Coding for bone diseases,” The Record, vol.23, no. 9, p. 27, 2011.

10 Different health problem associates with absence or decrease in one or more of these mechanical stimulations and will result in bone loss differently in anatomical location, quantity, velocity, and through different mechanisms.

18 Another study on 11 astronauts by Vico et alAnother study on 11 astronauts by Vico et al. showed greater bone losses occurred in cancellous bone compared to cortical bone. The mean decrease in cancellous BMD of the 11 astronauts was 11.4% after 6 months of spaceflight but the range of reduction varied from 0.4% to 23.4%. The astronaut who spent the longest time in space did not have the greatest bone loss.L. Vico, P. Collet, A. Guignandon et al., “Effects of longtermmicrogravity exposure on cancellous and cortical weightbearing bones of cosmonauts,” The Lancet, vol. 355, no. 9215,pp. 1607–1611, 2000.

25 The influence of genetic factors on skeletal development is most pronounced in young people. The impact of genetic factors diminishes with age because of the increasing impact of environmental and nutritional factors.Ralston, “Genetic determinants of bone mass . Principles of Bone Biology, vol. 2, pp. 1611– 1634, Elsevier, 3rd edition, 2008.

26 Skeletal growth and repair occur through bone remodeling which is a tightly regulated process.The normal bone mass is maintained during remodeling, based on the balance between bone formation and bone resorption.

28 However, because of certain events such as hormonal changes at menopause, the balance between bone formation andresorption is disturbed, and resorption occurs at a higher ratethan that of formation leading to osteoporosis.K. Matsuo and N. Irie, “Osteoclast-osteoblast communication,”Archives of Biochemistry and Biophysics, vol. 473, pp.201–209, 2008.Baron, L. Neff, and A. Vignery, “Differentiation andfunctional characteristics of osteoclasts,” Bone, vol. 6, p. 414, 2011

30 on osteoclast precursors triggers the maturation of osteoclasts, RANKL is found on the surface of osteoblasts and the interaction between RANKL and its receptors RANKon osteoclast precursors triggers the maturation of osteoclasts,thus inducing bone resorption.

31 INDUCED RANKL OPG AFTER MECHANICAL LOADING………involved in the reaction in mechanism of disuse osteoporosis.